Enthalpy, pH and kinetics experiments — NEET & JEE Questions

Question 1 · difficulty L1 · recall

In a simple calorimetry experiment, the heat absorbed by a solution is commonly estimated using

• A. $q=mc\Delta T$
• B. $q=m/c\Delta T$
• C. $q=c/(m\Delta T)$
• D. $q=m+c+\Delta T$

Question 2 · difficulty L2 · understanding

In a simple calorimetry experiment, why is the container insulated as well as practical?

• A. To reduce heat exchange with the surroundings
• B. To increase the number of moles reacting
• C. To make the reaction chemically reversible
• D. To force the thermometer to read exactly 0 °C

Question 3 · difficulty L2 · understanding

When measuring pH experimentally, a calibrated pH meter is generally more quantitative than

• A. a universal-indicator colour comparison
• B. a burette reading
• C. a balance measurement
• D. a stopwatch reading

Question 4 · difficulty L2 · understanding

In a rate experiment, why should variables other than the one being tested be kept constant?

• A. To isolate the effect of the chosen variable on reaction rate
• B. To make every reaction instantaneous
• C. To remove the need for repeated measurements
• D. To force the equilibrium constant to change

Question 5 · difficulty L3 · application

A reaction releases heat, but substantial heat escapes to the surroundings before the maximum temperature is recorded. How is the measured temperature rise affected?

• A. It is larger than the ideal temperature rise
• B. It is smaller than the ideal temperature rise
• C. It is unaffected because heat loss changes only pressure
• D. It must become negative for every exothermic reaction

Question 6 · difficulty L3 · application

In a kinetics experiment, the same visible endpoint is reached in 20 s in one run and 40 s in another. Using 1/time as a rate measure, how do the rates compare?

• A. Both runs have the same rate
• B. The 40 s run is twice as fast
• C. The 20 s run is twice as fast
• D. The 20 s run is four times as fast

Question 7 · difficulty L3 · application

A reaction warms 100 g of solution by 5.0 K. Taking $c=4.2\,\text{J g}^{-1}\text{K}^{-1}$, how much heat does the solution absorb?

• A. 210 J
• B. 420 J
• C. 2100 J
• D. 4200 J

Question 8 · difficulty L3 · application

In a kinetics experiment, 50 cm³ of gas is produced in 25 s. What is the average gas-production rate over this interval?

• A. 0.5 cm³ s$^{-1}$
• B. 2.0 cm³ s$^{-1}$
• C. 25 cm³ s$^{-1}$
• D. 75 cm³ s$^{-1}$

Question 9 · difficulty L4 · application

A calorimetry experiment gives a temperature rise smaller than the true value because heat escapes to the surroundings. For an exothermic reaction, the calculated magnitude of $\Delta H$ will most likely be

• A. underestimated
• B. overestimated
• C. unchanged exactly
• D. forced to zero

Question 10 · difficulty L4 · application

A pH meter gives 4.00 for a solution before dilution and 5.00 after dilution. The hydrogen-ion concentration after dilution is approximately

• A. ten times larger
• B. ten times smaller
• C. one hundred times larger
• D. unchanged